Conventional solar water heating systems generally consists of a separate solar collector and water store, with pipes connecting the collector(s) to and from store(s). These systems can be either active or passive, with the active systems using an electric pump, and the passive systems relying on buoyancy forces in the form of thermosiphonic action. The collector can be anything from a simple flat plate arrangement, requiring freeze protection, to the more costly evacuated (heat pipe) tube system. The collector is generally connected indirectly to the existing hot water installation and as such requires a twin coil hot water cylinder.
While solar water heating systems are very effective in some environments, in a large number of countries or regions of the world, a combination of low average daily insolation (incident solar radiation) levels and the need for freeze protection measures render commercially available domestic solar water heating systems unsuitable or prohibitively expensive.
In its simplest form the integrated collector storage solar water heater (ICSSWH) is a water tank painted black to absorb insolation. In the past variations consisted of one or more tanks, painted black or coated with a selective absorbing surface, within a well insulated box, possibly with reflectors and covered with single, double or even triple layers of glass, plastic or a combination of the two. Due to its simplicity, an integrated collector/storage system is easier to construct and install which reduces maintenance and capital costs. In most climates, the large thermal mass of the store provides inherent resistance to freezing. However the integrated unit has a significant problem due to its unique mode of operation.
The earliest systems suffered substantially from heat losses to ambient, especially at night-time and non-collection periods. This meant no matter how effective the unit was in collecting solar energy, unless the hot water was fully withdrawn at the end of the collection period, losses to ambient led to only luke warm water being available early the next day. This reduced the overall solar fraction rendering it less viable economically. Indeed this deficiency in the late nineteenth century led to the prominence of thermosiphonic solar water heaters with diurnal heat storage to the detriment of the ICSSWH system. To overcome excessive heat loss and be in a position to compete with the more established distributed solar water heater systems, the ICSSWH design has had to evolve and incorporate new and novel methods of improving performance.
The present invention has been developed to provide an improved solar water heating apparatus.